Data on this website are updated every Friday by 4pm. Due to different reporting schedules, case totals here may not always reflect those reported by local health departments. Updates during the off season (January-April) are less frequent.

April 17 - 23 is West Nile and Mosquito and Vector Control Awareness Week in California! This week highlights the importance of preventing mosquito bites and protecting Californians from mosquito-borne diseases. Stop by the "Fight the Bite" event at the State Capitol in Sacramento on Thursday, April 21st from 1:00 - 4:00pm for more information. Contact your local mosquito and vector control district to learn about events in your area.

215 human cases from 31 counties have tested positive for WNV in 2018.

horses

YTD: 11 Counties: 8

11 horses from 8 counties have tested positive for WNV in 2018.

dead birds

YTD: 501 Counties: 21

501 dead birds from 21 counties have tested positive for WNV in 2018.

mosquito samples

YTD: 1,963 Counties: 29

1,963 mosquito samples from 29 counties have tested positive for WNV in 2018.

A mosquito sample may contain up to 50 individual mosquitoes.

sentinel chickens

YTD: 163 Counties: 16

163 sentinel chickens from 16 counties have tested positive for WNV in 2018.

Be a West Nile Watcher

Help us track down the West Nile Virus by reporting all dead birds. You can submit an online report by clicking on the button on the right.

2003-2017 WNV Activity Summary

Element

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

Total

Human cases (fatal)

31 (0)

779 (29)

880 (19)

278 (7)

380 (21)

445 (15)

112 (4)

111 (6)

158 (9)

479 (20)

379 (15)

801 (31)

782 (53)

442 (19)

553 (44)

6,582 (292)

Horses

12

540

456

58

28

32

18

19

15

22

23

153

193

213

21

1,288

Dead birds

96

3,232

3,046

1,446

1,396

2,569

515

416

688

1,644

1,251

2,442

1,349

1,352

510

21,952

Mosquito samples

32

1,136

1,242

832

1,007

2,003

1,063

1,305

2,087

2849

2,528

3,340

3,329

3,528

3,371

29,652

Sentinel chickens

70

809

1,053

640

510

585

443

281

391

540

485

443

449

343

305

7,347

Squirrels

-

49

48

32

26

32

10

24

24

23

03

03

03

03

03

276

1 There were 20 imported human cases.
2 There were 3 imported horse cases.
3 Not monitored this year.

The California Mosquito-borne Virus Surveillance and Response Program works to protect Californians from mosquito-borne viruses through environmental monitoring, laboratory testing, mosquito control, and public outreach.